fs: littlefs: Use flash map macro in automount
fs: littlefs: Use flash map macro in automount

To identify the flash partition id, the macro DT_FIXED_PARTITION_ID()
was used previously.

Now the macro FLASH_AREA_ID() is used. This also supports the usecase
when a different flash map implementation is used that redefines the
macros in include/storage/flash_map.h, e.g. the nordic partition
manager.

Signed-off-by: Christian Taedcke <5dfb12f5b8690cb9c18e955016e7e3173b81d0d8@lemonbeat.com>

zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr